For some applications, such as adhesives, individual polymers do not possess the necessary combination of properties. For example, it has proved difficult to develop a single component adhesive that exhibits a good combination of properties, such as adhesion at low and high temperatures, short set time, thermal stability and mechanical strength. In an attempt to address this problem, individual polyolefins having different characteristics are often blended together in the hope of combining the positive attributes of the individual components. However, typically the result is a blend which displays an average of the individual properties of the individual polymers, including the less desirable properties. For example EP 0 527 589 discloses blends of flexible, low molecular weight amorphous polypropylene with higher molecular weight isotactic polypropylene to obtain compositions with balanced mechanical strength and flexibility. These compositions show better flexibility compared to that of the isotactic polypropylene alone, but are still lacking in other physical attributes. Physical blends also have the problems of inadequate miscibility. Unless the components are selected for their compatibility they can phase separate or low molecular weight components can migrate to the surface. Additional cost associated with compounding also makes these products less economically attractive.
Reactor blends, also called intimate blends (a composition comprising two or more polymers made in the same reactor or in a series of reactors) are often used to address these issues, however finding catalyst systems that will operate under the same environment to produce different polymers has been a challenge.
Multiple catalyst systems have been used in the past to produce reactor blends of various polymers and other polymer compositions. Reactor blends and other one-pot polymer compositions are often regarded as superior to physical blends of similar polymers. For example U.S. Pat. No. 6,248,832 discloses a polymer composition produced in the presence of one or more stereospecific metallocene catalyst systems and at least one non-stereospecific metallocene catalyst system. The resultant polymer has advantageous properties over the physical blends disclosed in EP 0 527 589 and U.S. Pat. No. 5,539,056.
Thus there has been interest in the art in developing multiple catalyst systems to produce new polymer compositions. For example, U.S. Pat. No. 5,516,848 discloses the use of two different cyclopentadienyl based transition metal compounds activated with alumoxane or non-coordinating anions. In particular, the examples disclose, among other things, catalyst compounds in combination, such as Me2Si(Me4C5)(N-c-C12H23)TiCl2 and rac-Me2Si(H4Ind)2ZrCl2, or Me2Si(Me4C5)(N-c-C12H23)TiCl2 and Me2Si(Ind)2HfMe2, (Ind=indenyl, H4Ind=tetrahydroindenyl, Me=methyl) activated with activators such as methylalumoxane or N,N-dimethyl anilinium tetrakis(pentafluorophenyl) borate, to produce polypropylenes having bimodal molecular weight distributions (Mw/Mn), varying amounts of isotacticity (from 12-52 wt % isotactic PP in the product in Ex 2, 3 and 4), and having weight average molecular weights over 100,000, and some even as high as 1,200,000 for use as thermoplastics. Likewise, U.S. Pat. No. 6,184,327 discloses a thermoplastic elastomer comprising a branched olefin polymer having crystalline sidechains and an amorphous backbone wherein at least 90 mol % of the sidechains are isotactic or syndiotactic polypropylene and at least 80 mole % of the backbone is atactic polypropylene produced by a process comprising: a) contacting, in solution, at a temperature from about 90° C. to about 120° C., propylene monomers with a catalyst composition comprising a chiral, stereorigid transition metal catalyst compound capable of producing isotactic or syndiotactic polypropylene; b) copolymerizing the product of a) with propylene and, optionally, one or more copolymerizable monomers, in a polymerization reactor using an achiral transition metal catalyst capable of producing atactic polypropylene; and c) recovering a branched olefin polymer. Similarly U.S. Pat. No. 6,147,180 discloses the synthesis of a thermoplastic polymer composition, which is produced by first polymerizing monomers to produce at least 40% vinyl terminated macromonomers and then copolymerizing the macromonomers with ethylene. In addition U.S. Pat. No. 6,323,284 discloses a method to produce thermoplastic compositions (mixtures of crystalline and amorphous polyolefin copolymers) by copolymerizing alpha-olefins and alpha, omega dienes using two separate catalyst systems.
Likewise others have experimented with multiple stage processes to produce new polymer compositions. For example EP 0 366 411 discloses a graft polymer having an EPDM backbone with polypropylene grafted thereto at one or more of the diene monomer sites through the use of a two-step process using a different Ziegler-Natta catalyst system in each step. This graft polymer is stated to be useful for improving the impact properties in blended polypropylene compositions.
US Pat. Appl. Pub. No. 2004/0138392, published Jun. 15, 2004, discloses a continuous process for producing an adhesive with a first component having a crystallinity of 5% or less and a second component having a crystallinity of 20% or more. The in-reactor blends show good balance among adhesion at both high and low temperature as well as set time. The process comprises 1) selecting a first catalyst component capable of producing a polymer having an Mw of 100,000 or less and a crystallinity of 5% or less under selected polymerization conditions; 2) selecting a second catalyst component capable of producing polymer having an Mw of 100,000 or less and a crystallinity of 20% or more at the selected polymerization conditions; 3) contacting, in a solvent and in a reaction zone under the selected polymerization conditions, the catalyst components in the presence of one or more activators with one or more C3-C20 olefins, and, optionally one or more diolefins; 4) at a temperature of greater than 100° C.; 5) at a residence time of 120 minutes or less; 6) wherein the ratio of the first catalyst to the second catalyst is from 1:1 to 50:1; 7) wherein the activity of the catalyst components is at least 50 kilograms of polymer per gram of the catalyst compounds; and wherein at least 80% of the olefins are converted to polymer; 8) withdrawing polymer solution from the reaction zone; 9) removing at least 10% solvent from the polymer solution; 10) quenching the reaction; 11) devolatilizing the polymer solution to form molten polymer; 12) combining the molten polymer and one or more additives in a static mixer; 13) removing the polymer combination from the static mixer; and 14) pelletizing or drumming the polymer combination. The selected stereo-specific catalysts are only capable of producing polymers with relatively low molecular weight and melting temperatures.
Likewise certain dual catalysts systems have been disclosed that produce branched polymers in single or multiple reactors that can be used in, inter alia, adhesive applications. See for example U.S. Pat. No. 7,223,822, US 2007/0293640, US 2004/0220336, US 2004/0220320, US 2004/0249046 and US 2004/0127614.
Another reference of interest is EP 0 728 773 A1.
It is highly desirable to have polyolefin based adhesives and thermoplastic polyolefins with high melting temperature for high temperature resistance applications. Using a catalyst capable of producing polymer with higher molecular weight and/or higher melting temperature also implies that the process can be operated at higher reaction temperature for better process economics.
According to the present invention, it has now been found certain N-bonded carbazol-9-yl substituted bridged bis-indenyl metallocene compounds, when combined with a suitable co-catalyst, are effective under solution polymerization conditions to produce olefin polymers with both high molecular weight and high crystallinity. Surprisingly, propylene based polymers produced using these N-bonded carbazol-9-yl substituted metallocene compounds exhibit significantly higher molecular weight than similar polymers produced using the equivalent N-bonded pyrrol-1-yl and indol-1-yl substituted metallocenes. Also surprising is the higher polymer melting point for propylene polymers produced using these carbazol-9-yl substituted metallocene compounds relative to those produced using the equivalent pyrrol-1-yl and indol-1-yl substituted metallocenes. Also surprising is the lower loss of polypropylene crystallinity when using these carbazol-9-yl substituted metallocene compounds at higher polymerization temperatures relative to the polypropylene produced using the equivalent pyrrol-1-yl and indol-1-yl substituted metallocenes. When combined with a catalyst capable of producing a polymer with a crystallinity of 10% or less, these N-bonded carbazol-9-yl substituted metallocene compounds produce in-reactor blends comprising a component having a crystallinity of 10% or less and a component having a crystallinity of 20% or more, wherein the composition and properties of the individual components are controlled so that the resultant blends, when optionally combined with small quantities of wax, tackifier and/or a functionalized polyolefin, exhibit an excellent balance of adhesive properties, including a good low temperature (such as −18° C. or lower) adhesion performance, short set time and a high strength at relatively low application viscosity.